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[bpf] disallow global_addr+off folding 

Wrong assembly code is generated for a simple program with
clang. If clang only produces IR and llc is used
for IR lowering and optimization, correct assembly
code is generated.

The main reason is that clang feeds default Reloc::Static
to llvm and llc feeds no RelocMode to llvm, where
for llc case, BPF backend picks up Reloc::PIC_ mode.
This leads different IR lowering behavior and clang
permits global_addr+off folding while llc doesn't.

This patch introduces isOffsetFoldingLegal function into
BPF backend and the function always return false.
This will make clang and llc behave the same for
the lowering.

Bug https://bugs.llvm.org//show_bug.cgi?id=33183
has more detailed explanation.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
llvm-svn: 304043
This commit is contained in:
Alexei Starovoitov 2017-05-26 22:32:41 +00:00
parent 23d2f0d77a
commit 3c585d3a8f
2 changed files with 12 additions and 1 deletions
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9
llvm/lib/Target/BPF/BPFISelLowering.cpp
View File

@ -132,6 +132,10 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = 128;
}
bool BPFTargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
return false;
}
SDValue BPFTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
switch (Op.getOpcode()) {
case ISD::BR_CC:
@ -496,8 +500,11 @@ const char *BPFTargetLowering::getTargetNodeName(unsigned Opcode) const {
SDValue BPFTargetLowering::LowerGlobalAddress(SDValue Op,
SelectionDAG &DAG) const {
auto N = cast<GlobalAddressSDNode>(Op);
assert(N->getOffset() == 0 && "Invalid offset for global address");
SDLoc DL(Op);
const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
const GlobalValue *GV = N->getGlobal();
SDValue GA = DAG.getTargetGlobalAddress(GV, DL, MVT::i64);
return DAG.getNode(BPFISD::Wrapper, DL, MVT::i64, GA);

4
llvm/lib/Target/BPF/BPFISelLowering.h
View File

@ -42,6 +42,10 @@ public:
// This method returns the name of a target specific DAG node.
const char *getTargetNodeName(unsigned Opcode) const override;
// This method decides whether folding a constant offset
// with the given GlobalAddress is legal.
bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;
MachineBasicBlock *
EmitInstrWithCustomInserter(MachineInstr &MI,
MachineBasicBlock *BB) const override;